x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 72 insertions, 0 deletions

diff --git a/drivers/eisa/virtual_root.c b/drivers/eisa/virtual_root.c
new file mode 100644
index 000000000..cd9515d9d
--- /dev/null
+++ b/drivers/eisa/virtual_root.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Virtual EISA root driver.
+ * Acts as a placeholder if we don't have a proper EISA bridge.
+ *
+ * (C) 2003 Marc Zyngier <maz@wild-wind.fr.eu.org>
+ */
+
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/eisa.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/init.h>
+
+#if defined(CONFIG_EISA_VLB_PRIMING)
+#define EISA_FORCE_PROBE_DEFAULT 1
+#else
+#define EISA_FORCE_PROBE_DEFAULT 0
+#endif
+
+static int force_probe = EISA_FORCE_PROBE_DEFAULT;
+static void virtual_eisa_release (struct device *);
+
+/* The default EISA device parent (virtual root device).
+ * Now use a platform device, since that's the obvious choice. */
+
+static struct platform_device eisa_root_dev = {
+	.name = "eisa",
+	.id   = 0,
+	.dev  = {
+		.release = virtual_eisa_release,
+	},
+};
+
+static struct eisa_root_device eisa_bus_root = {
+	.dev		= &eisa_root_dev.dev,
+	.bus_base_addr	= 0,
+	.res		= &ioport_resource,
+	.slots		= EISA_MAX_SLOTS,
+	.dma_mask	= 0xffffffff,
+};
+
+static void virtual_eisa_release (struct device *dev)
+{
+	/* nothing really to do here */
+}
+
+static int __init virtual_eisa_root_init (void)
+{
+	int r;
+
+	if ((r = platform_device_register (&eisa_root_dev)))
+		return r;
+
+	eisa_bus_root.force_probe = force_probe;
+
+	dev_set_drvdata(&eisa_root_dev.dev, &eisa_bus_root);
+
+	if (eisa_root_register (&eisa_bus_root)) {
+		/* A real bridge may have been registered before
+		 * us. So quietly unregister. */
+		platform_device_unregister (&eisa_root_dev);
+		return -1;
+	}
+
+	return 0;
+}
+
+module_param (force_probe, int, 0444);
+
+device_initcall (virtual_eisa_root_init);